The present invention relates to a printing plate assembly for use in flexographic printing applications, and more particularly, to an improved printing plate assembly including an integral carrier layer, cushion layer, and a photopolymer layer, which assembly provides a precise relief depth. The assembly is easily mounted on a flexographic cylinder and printed by an end user.
Flexographic printing is a form of relief printing which utilizes relief printing plates wrapped around a printing cylinder to transfer ink onto a substrate. Flexographic printing is primarily used in high-volume printing applications in the packaging and newspaper industries, and is typically used for printing substrates such as paper, plastic, foil, and corrugated board.
In recent years, flexographic printing has involved the use of printing plates formed from photopolymerizable compositions. Such photopolymerizable compositions typically comprise at least an elastomeric binder, a monomer, and a photoinitiator. Upon exposure of the photopolymer plate from the back to actinic radiation, polymerization of the photopolymerizable layer occurs. This step is typically referred to as a “back exposure” step in which the polymerized portion of the cross-section of the printing plate is formed, which is referred to as the “floor.” After the desired image of the printing plate is formed, typically by exposing the photopolymer layer from the front by actinic radiation, the unexposed areas of the plate are removed to form a relief image.
In addition to the printing plate, a separate carrier or attachment layer is typically used in conjunction with the printing plate which aids in attachment of the printing plate to the printing cylinder. The carrier layer is typically formed from a plastic material and includes tabs or strips at each end which are used to fix the printing plate to the printing cylinder after it is wrapped around the cylinder. Further, it is often desirable to include a separate cushion layer below the printing plate to provide an even impression across and around the cylinder. Such a cushion layer may comprise a foam layer or a foam tape which can be adhered to the printing plate.
Typically, the carrier layer and cushion layer are produced separately, and are adhered to each other and the printing plate using adhesive tapes. The three components are assembled together by an end user after the printing plate is exposed to create the desired relief image, and are then mounted on the flexographic press cylinder with the imaged plates positioned on the carrier for accurate registration with each other. However, such an assembly process is time consuming and subject to stacking tolerance problems due to tolerance variations in each individual layer in the assembly and positioning inaccuracy due to limitations of the plates and mounting devices. It would be desirable to be able to simplify the assembly process.
Accordingly, there is still a need in the art for an improved method of assembling a photopolymer printing plate, cushion layer, and carrier attachment for use in flexographic printing operations.